U.S. patent application number 15/372357 was filed with the patent office on 2017-03-23 for high speed, high terrestrial density global packet data mobile satellite system architectures.
The applicant listed for this patent is Hughes Network Systems, LLC. Invention is credited to John CORRIGAN, Channasandra RAVISHANKAR.
Application Number | 20170085329 15/372357 |
Document ID | / |
Family ID | 58283221 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170085329 |
Kind Code |
A1 |
RAVISHANKAR; Channasandra ;
et al. |
March 23, 2017 |
HIGH SPEED, HIGH TERRESTRIAL DENSITY GLOBAL PACKET DATA MOBILE
SATELLITE SYSTEM ARCHITECTURES
Abstract
A satellite communications system comprises multiple satellites
(e.g., a combination of LEO/MEO/GEO satellites). Multiple satellite
gateways communicate over channels of the satellites with remote
mobile user terminals. The mobile user terminals communicate with
the satellite gateways via associated satellite terminals that
interface with the satellites, or directly with the satellites.
Each mobile user terminal of a first group communicates with a
satellite gateway, over satellite channels, via an associated
satellite terminal. Each mobile user terminal of a second group
(e.g., in a remote rural area) communicates with a satellite
gateway directly over satellite channels. The mobile user terminals
of the first communicate with the satellite terminals locally via
S-band. The mobile user terminals of the second group communicate
directly over the satellite channels via Ku band or Ka Band. Each
of the satellite gateways communicates over satellite channels via
Ka band, Ku band, V-band or L-band.
Inventors: |
RAVISHANKAR; Channasandra;
(Clarksburg, MD) ; CORRIGAN; John; (Chevy Chase,
MD) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hughes Network Systems, LLC |
Germantown |
MD |
US |
|
|
Family ID: |
58283221 |
Appl. No.: |
15/372357 |
Filed: |
December 7, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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15186417 |
Jun 17, 2016 |
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15372357 |
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62264204 |
Dec 7, 2015 |
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62181062 |
Jun 17, 2015 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B 7/2125 20130101;
H04B 7/19 20130101; H04W 72/0453 20130101; H04B 7/18558
20130101 |
International
Class: |
H04H 40/90 20060101
H04H040/90; H04W 72/04 20060101 H04W072/04 |
Claims
1. A satellite communications system comprising: a plurality of one
or more of low earth orbit (LEO) satellites, medium earth orbit
(MEO) satellites and geosynchronous earth orbit (GEO) satellites; a
gateway node comprising one or more satellite gateways each
configured to communicate over respective channels of each of the
plurality of satellites via at least one respective gateway
antenna, an IP core network, and a border gateway configured to
communicate with one or more external IP networks; one or more
satellite terminals; and a plurality of mobile user terminals,
wherein the mobile user terminals, of a first subset of the
plurality of mobile user terminals, each is configured to
communicate with a respective one of the satellite gateways, over
one or more channels of the plurality of satellites, via an
associated one of the satellite terminals, and wherein the mobile
user terminals, of a second subset of the plurality of mobile user
terminals, each is configured to communicate with a respective one
of the satellite gateways directly over one or more channels of the
plurality of satellites; and wherein the mobile user terminals, of
the first subset of the plurality of mobile user terminals, each is
configured to communicate with the associated one of the satellite
terminals locally via an S-band channel; and wherein the mobile
user terminals, of the second subset of the plurality of mobile
user terminals, each is configured to communicate directly over the
one or more channels of the plurality of satellites, via one or
more of Ku band and Ka Band; and wherein each of the one or more
satellite gateways is configured to communicate over the respective
channels of each of the plurality of satellites via one or more of
Ka band, Ku band, V-band and L-band.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of the earlier filing
date under 35 U.S.C. .sctn.119(e) from U.S. Provisional Application
Ser. No. 62/264,204 (filed 2015 Dec. 7), which is incorporated
herein by reference in its entirety; and this application is a
continuation in part (CIP) from U.S. patent application Ser. No.
15/186,417 (filed 2016 Jun. 17), which claims the benefit of the
earlier filing date under 35 U.S.C. .sctn.119(e) from U.S.
Provisional Application Ser. No. 62/181,062 (filed 2015 Jun. 17),
the entireties of which are incorporated herein by reference.
BACKGROUND
[0002] Terrestrial communication systems continue to provide higher
and higher speed multimedia (e.g., voice, data, video, images,
etc.) services to end-users. Such services (e.g., Third Generation
(3G) and Fourth Generation Long Term Evolution (4G LTE) systems and
services) can also accommodate differentiated quality of service
(QoS) across various applications. To facilitate this, terrestrial
architectures are moving towards an end-to-end all-Internet
Protocol (IP) architecture that unifies all services, including
voice, over the IP bearer. In parallel, mobile satellite systems
are being designed to complement and/or coexist with terrestrial
coverage depending on spectrum sharing rules and operator choice.
With the advances in processing power of portable computers, mobile
phones and other highly portable devices, the average user has
grown accustomed to sophisticated applications (e.g., streaming
video, radio broadcasts, video games, etc.), which place tremendous
strain on network resources. Further, such users have grown to
expect ubiquitous global coverage. The Web as well as other
Internet services rely on protocols and networking architectures
that offer great flexibility and robustness; however, such
infrastructure may be inefficient in transporting Web traffic,
which can result in large user response time, particularly if the
traffic has to traverse an intermediary network with a relatively
large latency (e.g., a satellite network). Such high mobility,
enhanced processing power of devices, and growth of low-latency
applications, however, puts an immense strain on current
terrestrial and satellite communications systems.
[0003] What is needed, therefore, are approaches for
multi-satellite mobile satellite communications systems that
efficiently provide high speed and high quality packet data
services, and facilitate high terrestrial density.
SOME EXAMPLE EMBODIMENTS
[0004] Embodiments of the present invention advantageously address
the foregoing requirements and needs, as well as others, by
providing system architectures and designs for multi-satellite
mobile satellite communications systems that efficiently provide
high speed and high quality packet data services, and facilitate
high terrestrial density.
[0005] With processing satellites (e.g., geosynchronous Earth orbit
(GEO), medium Earth orbit (MEO), and low Earth orbit (LEO) and
satellites), IP packets and Layer 2 frames transmitted by user
terminals are recovered at the satellite and transmitted on the
gateway links and/or inter-satellite links. Similarly, in the
direction from network to user terminal, IP packets and Layer 2
frames transmitted by gateways are recovered at the satellite and
transmitted on the user links. The frequency and format of
transmission on gateway and user links may be different. In
addition, the transmission to and from user terminal on a user link
may be different. Similarly, the transmission to and from gateway
on a gateway link may be different. The architecture also permits
transmission from user terminal to another user terminal directly
without traversing through a gateway. Similarly, the architecture
permits direct gateway to gateway communication via the satellite
constellation. When LEO/MEO satellites are not processing
satellites (i.e., they are bent-pipe satellites), communication is
directly between user terminal and gateway with a frequency
translation between gateway links and user links.
[0006] In accordance with example embodiments, an overall network
architecture is shown in FIGS. 1A, 1B. The user terminal (UT) may
be in one of a multiplicity of beams in the user link. Satellites,
and therefore beams corresponding those satellites move (for
satellite-fixed beams) over the user terminal as the satellites of
the constellation move, even if the user terminal is not moving.
Accordingly, beam-to-beam and satellite-to-satellite handover are
required in this scenario. User terminals are typically equipped
with a tracking antenna that is preferably electronically steered.
However, the design does not preclude terminals using mechanical
steering. In another embodiment, the satellite attempts to steer
its antenna such that beams remain in the same place on the earth
surface (also called earth-fixed beams). In this case, there is no
need for beam-to-beam handover. The system also supports gateway to
gateway handover to cater to cases where a user terminal may be in
motion and it crosses from one gateway region to another. Gateway
to Gateway handover would also be necessary when a Gateway fails or
when the capacity of the gateway is such that it cannot accept any
additional sessions. As part of the above mentioned beam-to-beam,
satellite-to-satellite and gateway-to-gateway handovers, frequency
handovers occur in a multiple frequency reuse system. To this end,
the system design also supports frequency handover even when there
is no beam-to-beam, satellite-to-satellite and gateway-to-gateway
handovers; this will be the case when a frequency is deemed
unusable due to interference and/or when it is required to move a
terminal to a different frequency for resource usage efficiency
issues and for services such as IP multicast.
[0007] Certain system features are as follows: [0008] Powerful FEC
coding, near theoretical channel performance; [0009] Adaptive
Coding & Modulation (ACM) improves throughput every channel
condition; [0010] Power and spectrally efficient advanced
modulation; [0011] High spectral efficiency; [0012] High
terrestrial and satellite capacity density; [0013] High-speed data
services, and high quality of service (QoS) real-time or streaming
services; and [0014] Standard wireless and network protocols to
utilize commercial implementations and evolution.
[0015] Still other aspects, features, and advantages of the present
invention are readily apparent from the following detailed
description, simply by illustrating a number of particular
embodiments and implementations, including the best mode
contemplated for carrying out the present invention. The present
invention is also capable of other and different embodiments, and
its several details can be modified in various obvious respects,
all without departing from the spirit and scope of the present
invention. Accordingly, the drawing and description are to be
regarded as illustrative in nature, and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Embodiments of the present invention are illustrated by way
of example, and not by way of limitation, in the figures of the
accompanying drawings, in which like reference numerals refer to
similar elements, and in which:
[0017] FIG. 1A and FIG. 1B illustrate high-level architectures for
high speed/high quality packet data service GEO/MEO/LEO satellite
systems, according to example embodiments;
[0018] FIG. 1C illustrates a high-level architecture for the
network configuration of such a high speed/high quality packet data
service GEO/MEO/LEO satellite systems, according to example
embodiments;
[0019] FIG. 1D illustrates an example Ku band user or user terminal
(UT) link, according to example embodiments;
[0020] FIG. 2A illustrates the user plane protocol architecture for
satellite systems, according to example embodiments;
[0021] FIG. 2B illustrates the control plane protocol architecture
for satellite systems, according to example embodiments;
[0022] FIG. 3A illustrates a diagram depicting an example
constellation transition for a .pi./2 BPSK modulation, according to
example embodiments;
[0023] FIG. 3B illustrates a diagram depicting an example
constellation transition for a .pi./4 QPSK modulation, according to
example embodiments;
[0024] FIG. 3C illustrates a diagram depicting an example
constellation for a 16 APSK modulation, according to example
embodiments
[0025] FIG. 4A illustrates a typical satellite beam from an 18
meter reflector, according to example embodiments;
[0026] FIG. 4B illustrates a typical satellite beam in a K=1
scenario, according to example embodiments;
[0027] FIG. 4C illustrates a typical satellite beam in a K=4
scenario, according to example embodiments;
[0028] FIG. 4D illustrates a typical satellite beam in a K=9
scenario, according to example embodiments;
[0029] FIG. 5A illustrates an example of slow fading (e.g., in an
open environment), according to example embodiments;
[0030] FIG. 5B illustrates an example of fast fading (e.g., in an
open environment), according to example embodiments;
[0031] FIG. 5C illustrates an example of fading (e.g., in a typical
suburban environment), according to example embodiments;
[0032] FIG. 5D illustrates an example of fading (e.g., in a typical
urban environment), according to example embodiments;
[0033] FIG. 6A illustrates a comparison of example vocoders (from
the website http://www.dvsinc.com/papers/eval_results.htm);
[0034] FIGS. 6B(i), 6B(ii), 6B(iii), 6B(iv) illustrate a comparison
of example AMR and AMBE+2 vocoders (P25: AMBE+2 vocoder at 4.4 kbps
source rate; A12.2: AMR 12.2 kbps source rate; A7.4: AMR 7.4 kbps
source rate);
[0035] FIG. 7A illustrates an example of UT return link
synchronization where the transmissions of two different UTs
overlap at the satellite according to example embodiments;
[0036] FIG. 7B illustrates an example UT return link
synchronization scheme, according to example embodiments;
[0037] FIG. 8A illustrates synchronization and half-duplex
operation for a beam level, position unaware scheduler, according
to example embodiments;
[0038] FIG. 8B illustrates synchronization and half-duplex
operation for a terminal position aware scheduler according to
example embodiments;
[0039] FIG. 9 illustrates a further example synchronization scheme,
according to example embodiments;
[0040] FIG. 10 illustrates an example terminal schematic and sleep
states, according to example embodiments;
[0041] FIG. 11A illustrates the rate of change of delay on LEO
links, according to example embodiments;
[0042] FIG. 11B illustrates the rate of change of Doppler on LEO
links, according to example embodiments;
[0043] FIG. 11C illustrates uncertainty in delay as a function of
terminal sleep duration, according to example embodiments;
[0044] FIG. 11D illustrates uncertainty in Doppler as a function of
terminal sleep duration, according to example embodiments;
[0045] FIG. 12A illustrates the ergodic capacity of a Rayleigh
fading SISO channel (dotted line) compared to the Shannon capacity
of a SISO channel (solid line);
[0046] FIG. 12B illustrates the Shannon capacity of a SISO channel
(dotted line) compared to the ergodic capacity of a Rayleigh fading
MIMO channel (solid line);
[0047] FIG. 12C illustrates a comparison between channel capacity
of SISO, SIMO and MIMO channels;
[0048] FIG. 13 illustrates a view of OFDM as linear precoding,
according to example embodiments;
[0049] FIG. 14A illustrates an example of Dual Polarization
SU-MIMO;
[0050] FIG. 14B illustrates an example of SU-MIMO with
geographically separated ground stations;
[0051] FIG. 14C (Statistical Modeling of Dual-Polarized MIMO Land
Mobile Satellite Channels, Konstantinos P. Liolis, et al., IEEE
Transactions on Communications, November 2010) illustrates an
example of Dual Polarization MIMO over Land Mobile Satellite
Systems;
[0052] FIG. 15A illustrates a channel capacity example in a rural
environment;
[0053] FIG. 15B illustrates a channel capacity example in a
suburban environment;
[0054] FIG. 15C illustrates a channel capacity example in a
suburban environment;
[0055] FIG. 15D (Michael Cheffena, Fernando Perez Fontan, Frederic
Lacoste, Erwan Corbel, Henri-Jose Mametsa and Guillaume Carrie,
IEEE Trans Ant and Propagation) illustrates modeling and
performance evaluation of a land mobile satellite dual polarized
MIMO channel along roadside trees;
[0056] FIG. 16A and FIG. 16B (Liolis, et al., EURASIP WCN, 2007)
illustrate a multi-satellite MIMO example at Ka band and above;
and
[0057] FIG. 16C illustrates channel capacity of a dual satellite
MIMO.
DETAILED DESCRIPTION
[0058] System architectures and associated processes for providing
high speed and high quality packet data services via a GEO/MEO/LEO
satellite system are described. In the following description, for
the purposes of explanation, numerous specific details are set
forth in order to provide a thorough understanding of the
invention. It is apparent, however, that the invention may be
practiced without these specific details or with an equivalent
arrangement. In other instances, well-known structures and devices
are shown in block diagram form in order to avoid unnecessarily
obscuring the invention.
[0059] As will be appreciated, a module or component (as referred
to herein) may be composed of software component(s), which are
stored in a memory or other computer-readable storage medium, and
executed by one or more processors or CPUs of the respective
devices. As will also be appreciated, however, a module may
alternatively be composed of hardware component(s) or firmware
component(s), or a combination of hardware, firmware and/or
software components. Further, with respect to the various example
embodiments described herein, while certain of the functions are
described as being performed by certain components or modules (or
combinations thereof), such descriptions are provided as examples
and are thus not intended to be limiting. Accordingly, any such
functions may be envisioned as being performed by other components
or modules (or combinations thereof), without departing from the
spirit and general scope of the present invention. Moreover, the
methods, processes and approaches described herein may be
processor-implemented using processing circuitry that may comprise
one or more microprocessors, application specific integrated
circuits (ASICs), field programmable gate arrays (FPGAs), or other
devices operable to be configured or programmed to implement the
systems and/or methods described herein. For implementation on such
devices that are operable to execute software instructions, the
flow diagrams and methods described herein may be implemented in
processor instructions stored in a computer-readable medium, such
as executable software stored in a computer memory store.
[0060] Further, terminology referring to computer-readable media or
computer media or the like as used herein refers to any medium that
participates in providing instructions to the processor of a
computer or processor module or component for execution. Such a
medium may take many forms, including but not limited to
non-transitory non-volatile media and volatile media. Non-volatile
media include, for example, optical disk media, magnetic disk media
or electrical disk media (e.g., solid state disk or SDD). Volatile
media include dynamic memory, such random access memory or RAM.
Common forms of computer-readable media include, for example,
floppy or flexible disk, hard disk, magnetic tape, any other
magnetic medium, CD ROM, CDRW, DVD, any other optical medium,
random access memory (RAM), programmable read only memory (PROM),
erasable PROM, flash EPROM, any other memory chip or cartridge, or
any other medium from which a computer can read data.
[0061] Various forms of computer-readable media may be involved in
providing instructions to a processor for execution. For example,
the instructions for carrying out at least part of the present
invention may initially be borne on a magnetic disk of a remote
computer. In such a scenario, the remote computer loads the
instructions into main memory and sends the instructions over a
telephone line using a modem. A modem of a local computer system
receives the data on the telephone line and uses an infrared
transmitter to convert the data to an infrared signal and transmit
the infrared signal to a portable computing device, such as a
personal digital assistance (PDA) and a laptop. An infrared
detector on the portable computing device receives the information
and instructions borne by the infrared signal and places the data
on a bus. The bus conveys the data to main memory, from which a
processor retrieves and executes the instructions. The instructions
received by main memory may optionally be stored on storage device
either before or after execution by processor.
Architecture.
[0062] FIG. 1A and FIG. 1B illustrate high-level architectures for
high speed/high quality packet data service GEO/MEO/LEO satellite
systems, and FIG. 1C illustrates a high-level architecture for the
network configuration of such a high speed/high quality packet data
service GEO/MEO/LEO satellite systems, according to example
embodiments. FIG. 1D illustrates an example Ku band user or user
terminal (UT) link, according to example embodiments. As
illustrated by the drawings of FIG. 1, by way of example, the
terminal/user-links may comprise one or more of Ku band and Ka band
links (and may alternatively or additionally comprise one or more
of L band and S band links), and the Gateway links may comprise one
or more of Ku band, Ka Band, Q band and V band links. Other
frequencies that are mutually exclusive may also be used in Gateway
link and user links. As further shown in FIG. 1, Satellite Gateways
are connected via terrestrial links or via the existing satellite
constellation links (e.g., via LEO/MEO satellite links or via a GEO
satellite system). The IP Core network resembles that of a
classical 4G-LTE network with the Border Gateway playing the role
of the packet data network (PDN) Gateway (PGW) of LTE core network.
Other elements that have a correspondence to 4G LTE core network
include Subscription server (equivalent to the Home Subscription
Server--HSS), Management Server (equivalent of MME) and Security
Server (equivalent to AuC). Although the Serving Gateway (SGW) is
not explicitly shown, it is expected to be part of the Satellite
Gateway and/or PGW.
[0063] FIG. 2A illustrates the user plane protocol architecture for
satellite systems, according to example embodiments, and FIG. 2B
illustrates the control plane protocol architecture for satellite
systems, according to example embodiments.
Bearer Attributes.
[0064] According to example embodiments, a wide range of bearers
may be employed depending on resource availability, demand and
terminal capability. By way of example, symbol rates may range from
11.7 killa-symbols-per-second (ksps) to 17.4
Mega-symbols-per-second (Msps), bandwidths may range from 13.5 kHz
to 20 MHz, modulation schemes comprise .pi./2 BPSK, .pi./4 QPSK,
16-APSK, 32-APSK, 64-QAM, coding schemes may comprise LDPC and
convolutional codes, code rates may comprise 1/2, 4/7, 5/8, 2/3, %,
4/5, 5/6, 9/10, spectral efficiency with single polarization up to
4.2 bits/s/Hz, and effective spectral efficiency with two
polarizations up to 8.4 bits/s/Hz. Such bearers are designed to
support a variety of terminal types, data rates, traffic types and
efficient resource utilization. Similar to terrestrial systems, the
spectral efficiency requires higher satellite power to close links
at higher symbol rates.
Modulations.
[0065] According to example embodiments, power and spectrally
efficient modulations are employed, such as .pi./2 BPSK, .pi./4
QPSK, 8 PSK, 16-APSK, 32-APSK, 64-QAM. FIG. 3A illustrates a
diagram depicting an example constellation transition for a .pi./2
BPSK modulation, according to example embodiments. FIG. 3B
illustrates a diagram depicting an example constellation transition
for a .pi./4 QPSK modulation, according to example embodiments.
FIG. 3C illustrates a diagram depicting an example constellation
for a 16 APSK modulation, according to example embodiments.
Further, the following table shows peak-two-average power ratios
(PAPR) for the modulation schemes:
TABLE-US-00001 .pi./2 .pi./4 16 16 32- BPSK BPSK QPSK QPSK QAM APSK
APSK 3.85 1.84 3.86 3.17 6.17 4.72 5.91
Link Analyses.
[0066] According to example embodiments, for the link analyses, the
user terminal (UT) antenna gain it is assumed to be approximately 3
dBi (e.g., for a stub antenna). Further, the UT antenna power is
assumed to be approximately 28 dBm, the antenna loss is assumed to
be approximately 1 dB, and total spectrum is assumed to be
approximately 34 MHz in L band. Alternatively, improved spectral
efficiency may be achieved using left-hand circular polarized
(LHCP) and right-hand circular polarized (RHCP) antennas. Further,
the return bearers for voice over IP (VoIP) are assumed to be at a
symbol rate of 11.7 ksps, using .pi./4 QPSK and 8 PSK for 2.4 and
9.6 kbps vocoder rates. Moreover, narrowband AMR vocoder rates span
from 4.75 kbps to 12.2 kbps, and newer generation vocoders (such as
AMBE+2) may be employed to provide equivalent or better quality
between 2.4 and 9.6 kbps. Additionally, AMR-WB used in HD voice
goes up to 23.3 kbps, and although the link analyses shown in the
below tables are not performed for 23.3 kbps, the analyses suggest
that it would be possible to go to about 12.6 kbps wideband with
little or no margin in return link. Lastly, the satellite antenna
gain to noise temperature (G/T) is assumed to be approximately 20
dB/K, and the satellite carrier to noise or interference ratio
(C/I) is assumed as variable from 12 dB to 19 dB.
[0067] The following table illustrates the link analysis for the
return link-voice:
TABLE-US-00002 Vocoder Data Rate kbps 2.4 9.6 UT EIRP- 28 dBm PA, 3
dBi, antenna, dBW 0 0 1 dB loss Uplink Frequency GHz 1.64 1.64
Satellite Altitude km 35786 35786 User Terminal Elevation deg 30 30
Slant Range km 38611.6 38611.6 Received Power at SAT antenna input
dBW -203.4 -196.0 Free Space loss dB 188.5 188.5 Fade Margin dB
14.40 7.00 Polarization and Pointing Loss dB 0.5 0.5 Satellite G/T
dB/K 20.00 20.00 Symbol Rate ks/s 11.7 11.7 uplink C/No dB-Hz 45.2
52.6 Feederlink C/No (assumed) dB-Hz 60.6 60.6 Overall C/No dB-Hz
45.1 52.0 Received C/N dB 4.42 11.30 C/I dB 12 12 Received C/(N +
I) dB 3.72 8.62 Modulation pi/4 QPSK 8 PSK FEC Code Rate (approx.)
3/5 2/3 Required C/N dB 3.6 8.5 Excess Link Margin dB 0.12 0.12
Carrier Bandwidth kHz 13.455 13.455 calls per carrier 4 2 Voice
calls per MHz 296 148
[0068] The following table illustrates the link analysis for the
forward link-voice-narrowband channelization:
TABLE-US-00003 Vocoder Data Rate kbps 2.4 9.6 Required Satellite
EIRP per carrier dBW 36.6 43.4 Downlink Frequency GHz 1.56 1.56
Satellite Altitude km 35786 35786 User Terminal Elevation deg 30 30
Slant Range km 38611.6 38611.6 Received Power at UT antenna input
dBW -156.9 -150.1 Free Space loss dB 188.0 188.0 Avg. Link Margin
dB 5.00 5.00 Polarization and Pointing Loss dB 0.5 0.5 UT Antenna
Gain (customer input) dBi 3.0 3.0 Antenna Losses (assumed) dB 1.0
1.0 Effective User Terminal G/T@290K dB/K -23.62 -23.62 Downlink
C/No dB-Hz 48.0 54.8 Symbol Rate ks/s 23.4 23.4 Received C/N dB
4.34 11.14 C/I dB 12.0 12.0 Received C/(N + I) dB 3.66 8.54
Modulation pi/4 QPSK 8-PSK FEC Code Rate (approx.) 3/5 2/3 Required
C/N dB 3.6 8.5 Excess Link Margin dB 0.06 0.04 Carrier Bandwidth
kHz 26.91 26.91 calls per carrier 8 4 Voice calls per MHz 296 148
Spectral Efficiency bit/s/Hz 0.71 1.42
[0069] Link Analyses--MEO Satellite Constellation.
[0070] According to example embodiments, for the link analyses with
a MEO satellite constellation, the UT antenna gain it is assumed to
be approximately 3 dBi (e.g., for a stub antenna). Further, the UT
antenna power is assumed to be approximately 28 dBm, the antenna
loss is assumed to be approximately 1 dB, and total spectrum is
assumed to be approximately 34 MHz in L band. Alternatively,
improved spectral efficiency may be achieved using LHCP and RHCP
antennas. Further, the return bearers for VoIP are assumed to be at
a symbol rate of 11.7 ksps, using .pi./4 QPSK, 8 PSK and 32 APSK
for 2.4, 7.4 and 9.6 kbps vocoder rates. Moreover, narrowband AMR
vocoder rates span from 4.75 kbps to 12.2 kbps, and newer
generation vocoders (such as AMBE+2) may be employed to provide
equivalent or better quality between 2.4 and 9.6 kbps.
Additionally, AMR-WB used in HD voice goes up to 23.3 kbps, and
although the link analyses shown in the below tables are not
performed for 23.3 kbps, the analyses suggest that it would be
possible to go to about 12.6 kbps wideband with little or no margin
in return link. Further, the satellite G/T is assumed to be
approximately 14 dB/K and 20 dB/K, and the satellite C/I is assumed
as variable from 12 dB to 21 dB. The orbit height is assumed at
approximately 10,000 km, with two orthogonal orbits, 45 degree
inclination angle, five satellites per orbit.
[0071] The following table illustrates the link analysis for the
return link-voice-MEO satellite with G/T=20 dB/K:
TABLE-US-00004 Vocoder Data Rate kbps 2.4 9.6 UT EIRP- 28 dBm PA, 3
dBi, antenna, dBW 0 0 1 dB loss Uplink Frequency GHz 1.64 1.64
Satellite Altitude km 10000 10000 User Terminal Elevation deg 30 30
Slant Range km 12229.5 12229.5 Received Power at SAT antenna input
dBW -196.0 -186.3 Free Space loss dB 178.5 178.5 Fade Margin dB
17.00 7.30 Polarization and Pointing Loss dB 0.5 0.5 Satellite G/T
dB/K 20.00 20.00 Symbol Rate ks/s 11.7 11.7 uplink C/No dB-Hz 52.6
62.3 Feederlink C/No (assumed) dB-Hz 60.6 60.6 Overall C/No dB-Hz
52.0 58.4 Received C/N dB 11.29 17.68 C/I dB 12 21 Received C/(N +
I) dB 8.62 16.02 Modulation 8 PSK 32-APSK FEC Code Rate (approx.)
2/3 4/5 Required C/N dB 8.5 16 Excess Link Margin dB 0.12 0.02
Carrier Bandwidth kHz 13.46 13.46 calls per carrier 8.00 4.00 Voice
calls per MHz 592 296
[0072] The following table illustrates the link analysis for the
return link-voice-MEO satellite with G/T=14 dB/K (half the size of
the antenna on a geosynchronous Earth orbit (GEO) satellite):
TABLE-US-00005 Vocoder Data Rate kbps 2.4 7.2 UT EIRP- 28 dBm PA, 3
dBi, antenna, dBW 0 0 1 dB loss Uplink Frequency GHz 1.64 1.64
Satellite Altitude km 10000 10000 User Terminal Elevation deg 30 30
Slant Range km 12229.5 12229.5 Received Power at SAT antenna input
dBW -190.0 -186.3 Free Space loss dB 178.5 178.5 Fade Margin dB
11.00 7.30 Polarization and Pointing Loss dB 0.5 0.5 Satellite G/T
dB/K 14.00 14.00 Symbol Rate ks/s 11.7 11.7 uplink C/No dB-Hz 52.6
56.3 Feederlink C/No (assumed) dB-Hz 60.6 60.6 Overall C/No dB-Hz
52.0 54.9 Received C/N dB 11.29 14.25 C/I dB 12 21 Received C/(N +
I) dB 8.62 13.42 Modulation 8-PSK 16 APSK FEC Code Rate (approx.)
2/3 3/4 Required C/N dB 8.5 13.4 Excess Link Margin dB 0.12 0.02
Carrier Bandwidth kHz 13.46 13.46 calls per carrier 8.00 4.00 Voice
calls per MHz 592 296
[0073] According to example embodiments, for the gateway links,
assuming 3 GHz of Ka spectrum availability on each polarization,
this would cover the equivalent of six user beams. By way of
example, the system may deploy 10 gateways to cover a 60 beam
operation, with 10 tracking antennas on the satellite for the
feeder link. By way of further example, the Gateway locations can
be determined for best availability. According to further example
embodiments, the number of gateways can be reduced by employing
processing satellites and/or employing additional spectrum (e.g.,
V/Q bands) and interference cancellation.
[0074] According to further example embodiments, with regard to the
links between the satellite terminal and the handset (e.g., the UT
to the user mobile handset), the satellite terminal may distribute
data locally to urban cells as per demand using S-band. As many
satellite terminals may be used as the number of cells that are
needed in urban/semi-urban/rural environments. Waveforms and
protocols may be based on 4G/5G to take advantage of recent
developments in terrestrial equipment and systems. Further, the
handset may be S-band and L-band capable, where it may use S-band
when S-band signals are available (e.g., when the hand-held can
communicate with the satellite terminal), and otherwise may use
L-band directly with the satellite (e.g., in rural environments
satellite terminals may not yet be deployed in the vicinity). Use
of L-band (instead of S-band) is also to avoid interference from
S-band handsets. In this context, the satellite would be capable of
both Ku band and L band communications.
[0075] The following table illustrates the link analysis for the
forward link-voice-narrowband channelization-MEO satellite
constellation:
TABLE-US-00006 Data Rate kbps 2.4 9.6 Required Satellite EIRP per
carrier dBW 33.4 41.3 Downlink Frequency GHz 1.56 1.56 Satellite
Altitude km 10000 10000 User Terminal Elevation deg 30 30 Slant
Range km 12229.5 12229.5 Received Power at UT antenna input dBW
-150.2 -142.3 Free Space loss dB 178.1 178.1 Avg. Link Margin dB
5.00 5.00 Polarization and Pointing Loss dB 0.5 0.5 UT Antenna Gain
(customer input) dBi 3.0 3.0 Antenna Losses (assumed) dB 1.0 1.0
Effective User Terminal G/T@290K dB/K -23.62 -23.62 Downlink C/No
dB-Hz 54.8 62.7 Symbol Rate ks/s 23.4 23.4 Received C/N dB 11.13
19.03 C/I dB 12.0 19.0 Received C/(N + I) dB 8.53 16.00 Modulation
8-PSK 32-APSK FEC Code Rate (approx.) 2/3 4/5 Required C/N dB 8.5
16 Excess Link Margin dB 0.03 0.00 Carrier Bandwidth kHz 26.91
26.91 calls per carrier 16 8 Voice calls per MHz 592 296 Spectral
Efficiency bit/s/Hz 1.42 2.84
[0076] The following table illustrates the link analysis for a LEO
satellite constellation:
TABLE-US-00007 LEO Data Rate per carrier per pol Gbps 1.3832
Required Satellite EIRP per carrier dBW 35.4 Downlink Frequency GHz
12 Satellite Altitude km 900 User Terminal Elevation deg 70 Slant
Range km 950.0 Received Power at UT antenna input dBW -140.7 Free
Space loss dB 173.6 Avg. Link Margin dB 2.00 Polarization and
Pointing Loss dB 0.5 UT Antenna Gain (customer input) dBi Antenna
Losses (assumed) dB Effective User Terminal G/T@100K; 1 m dB/K 15
array Downlink C/No dB-Hz 102.9 Symbol Rate ks/s 455000 Received
C/N dB 16.33 C/I dB 14.0 Received C/(N + I) dB 12.00 Modulation
16-APSK FEC Code Rate (approx.) 3/4 Required C/N dB 12 Excess Link
Margin dB 0.00 Carrier Bandwidth kHz 500000 Spectral Efficiency per
pol bit/s/Hz 0.00 Number of carriers per satellite 120 Throupghput
per satellite Gbps 165.984
Voice Capacity.
[0077] According to example embodiments, the provided satellite
system architectures and designs support upwards of 296 voice calls
per MHz of L-band bandwidth (assuming 2.4 kbps voice), and upwards
of 148 calls at 9.6 kbps with lower link margin. Further, in view
the fact that an AMR type vocoder is employed (narrowband or
wideband), the higher vocoder rate will be supported when channel
conditions are good (therefore requires less margin). Further, a
cluster of satellite beams using 34 MHz of bandwidth, therefore,
allows about 10,000 simultaneous voice calls at 2.4 kbps. The total
system capacity will depend on the number of times the 34 MHz can
be reused, where, in the forward link, it will also be limited by
the total satellite power (e.g., each voice call requires
approximately 27.6 dBW of satellite EIRP for a terminal with 3 dBi
antenna and 28 dBm PA output). For example, when the 34 MHz is used
20 times (for reuse factor of 9, this implies 180 beams) in the
coverage area, the simultaneous voice capacity is approximately
200,000 calls. In terms of satellite power this would require
approximately 80 dBW of satellite EIRP.
Spectral Efficiency.
[0078] The following table illustrates a comparison of spectral
efficiency between .pi./4 QPSK at rate 3/5 and 32-APSK at rate
4/5:
TABLE-US-00008 2.4 k/s 2.4 k/s vocoder vocoder Data Rate kbps 2.4
84.24 Required Satellite EIRP per carrier dBW 36.6 51.3 Downlink
Frequency GHz 1.56 1.56 Satellite Altitude km 35786 35786 User
Terminal Elevation deg 30 30 Slant Range km 38611.6 38611.6
Received Power at UT antenna input dBW -156.9 -142.2 Free Space
loss dB 188.0 188.0 Avg. Link Margin dB 5.00 5.00 Polarization and
Pointing Loss dB 0.5 0.5 UT Antenna Gain (customer input) dBi 3.0
3.0 Antenna Losses (assumed) dB 1.0 1.0 Effective User Terminal
G/T@290K dB/K -23.62 -23.62 Downlink C/No dB-Hz 48.0 62.7 Symbol
Rate ks/s 23.4 23.4 Receive C/N dB 4.34 19.04 C/I dB 12.0 19.0
Received C/(N + I) dB 3.66 16.01 Modulation pi/4 QPSK 32-APSK FEC
Code Rate (approx.) 3/5 4/5 Required C/N dB 3.6 16 Excess Link
Margin dB 0.06 0.01 Carrier Bandwidth kHz 26.91 26.91 calls per
carrier 8 35.1 Voice calls per MHz 296 1299 Spectral Efficiency
bit/s/Hz 0.71 3.13
[0079] According to example embodiments, waveforms with higher
spectral efficiency (e.g., 32-APSK with Rate 4/5 or even higher in
the forward link) may be employed. Such a scheme can deliver
spectral efficiency of 3.13 bits/s/Hz. Further, using both
polarizations (left hand and right hand) in the forward link, the
effective spectral efficiency can be increased to 6.26 bits/s/Hz.
Higher code rates such as Rate 9/10 and higher order modulation
such as 64-QAM can further improve spectral efficiency. As seen
from the analyses of the foregoing table, this comes with an
increase in satellite power--for example, about 15 dB increase in
power needed for about 6 dB increase in spectral efficiency.
Furthermore, the increase Es/No requirement implies better
management of interference.
[0080] According to example embodiments, forward link throughput is
limited based on satellite power. For example, where the satellite
can deliver a maximum of 80 dBW of EIRP per polarization, a total
capacity of about 150 Mbps per polarization can be obtained with a
spectral efficiency of 3.13 b/s/Hz/pol, whereas with a spectral
efficiency of 1.03 b/s/Hz/pol, a total capacity of about 1 Gbps per
polarization can be obtained--which reflects a system capacity
versus per channel capacity trade-off--as illustrated in the
following Table:
TABLE-US-00009 Data Rate kbps 15649.2 5164.236 Required Satellite
EIRP per carrier dBW 70.2 57 Downlink Frequency GHz 1.56 1.56
Satellite Altitude km 35786 35786 User Terminal Elevation deg 30 30
Slant Range km 38611.6 38611.6 Received Power at UT antenna input
dBW -120.3 -133.5 Free Space loss dB 188.0 188.0 Avg. Link Margin
dB 2.00 2.00 Polarization and Pointing Loss dB 0.5 0.5 UT Antenna
Gain (customer input) dBi 3.0 3.0 Antenna Losses (assumed) dB 1.0
1.0 Effective User Terminal G/T@290K dB/K -23.62 -23.62 Downlink
C/No dB-Hz 84.6 71.4 Symbol Rate ks/s 4347 4347 Received C/N dB
18.25 5.05 C/I dB 20.0 9.0 Received C/(N + I) dB 16.03 3.58
Modulation 32-APSK pi/4 QPSK FEC Code Rate (approx.) 4/5 2/3
Required C/N dB 16 3.5 Excess Link Margin dB 0.03 0.06 Carrier
Bandwidth kHz 5000 5000 Spectral Efficiency per pol bit/s/Hz 3.13
1.03
High Speed Data Example.
[0081] According to example embodiments, using 5 MHz bandwidth per
beam, more than 15 Mbps of throughput is achieved yielding a
spectral efficiency of 3.13 bits/s/Hz per polarization, which,
using two polarizations, would achieve a spectral efficiency of
6.26 bit/s/Hz. Further, the satellite EIRP would be about 70 dBW
per carrier, the C/I requirement would be 19 dB or higher.
According to further example embodiments, interference mitigation
schemes could be employed to achieve such high C/I with small reuse
factor. The following table illustrates such a high speed data
example, in accordance with example embodiments:
TABLE-US-00010 Data Rate kbps 15649.2 Required Satellite EIRP per
carrier dBW 70.2 Downlink Frequency GHz 1.56 Satellite Altitude km
35786 User Terminal Elevation deg 30 Slant Range km 38611.6
Received Power at UT antenna input dBW -120.3 Free Space loss dB
188.0 Avg. Link Margin dB 2.00 Polarization and Pointing Loss dB
0.5 UT Antenna Gain (customer input) dBi 3.0 Antenna Losses
(assumed) dB 1.0 Effective User Terminal G/T@290K dB/K -23.62
Downlink C/No dB-Hz 84.6 Symbol Rate ks/s 4347 Received C/N dB
18.25 C/I dB 20.0 Received C/(N + I) dB 16.03 Modulation 32-APSK
FEC Code Rate (approx.) 4/5 Required C/N dB 16 Excess Link Margin
dB 0.03 Carrier Bandwidth kHz 5000 Spectral Efficiency per pol
bit/s/Hz 3.13
[0082] According to example embodiments, with a MEO satellite
constellation, using 5 MHz bandwidth per beam, more than 20 Mbps of
throughput is achieved yielding a spectral efficiency of 4.17
bits/s/Hz per polarization, which, using two polarizations, would
achieve a spectral efficiency of 8.34 bit/s/Hz. Further, the
satellite EIRP would be about 67.5 dBW per carrier, the C/I
requirement would be 23 dB or higher. According to further example
embodiments, interference mitigation schemes could be employed to
achieve such high C/I with small reuse factor. The following table
illustrates such a high speed data example with a MEO
constellation, in accordance with example embodiments:
TABLE-US-00011 Data Rate kbps 20865.6 Required Satellite EIRP per
carrier dBW 67.5 Downlink Frequency GHz 1.56 Satellite Altitude km
10000 User Terminal Elevation deg 30 Slant Range km 12229.5
Received Power at UT antenna input dBW -113.1 Free Space loss dB
178.1 Avg. Link Margin dB 2.00 Polarization and Pointing Loss dB
0.5 UT Antenna Gain (customer input) dBi 3.0 Antenna Losses
(assumed) dB 1.0 Effective User Terminal G/T@290K dB/K -23.62
Downlink C/No dB-Hz 91.9 Symbol Rate ks/s 4347 Received C/N dB
25.54 C/I dB 23.0 Received C/(N + I) dB 21.08 Modulation 64-APSK
FEC Code Rate (approx.) 4/5 Required C/N dB 21 Excess Link Margin
dB 0.08 Carrier Bandwidth kHz 5000 Spectral Efficiency per pol
bit/s/Hz 4.17
Terrestrial/Satellite Capacity Density.
[0083] According to example embodiments, the following table
illustrates an example of the terrestrial/satellite capacity
density (to get comparable capacity density, as terrestrial system
in a typical satellite system with 80 km beam radius, each
satellite beam requires to support about 77 Gbps throughput):
TABLE-US-00012 Attribute Value Units hexagonal area with cell
radius of 2 km 10.3923 sq km circular area with cell radius of 2 km
12.56637 sq km circular area with beam radius of 80 km 20106.19 sq
km avg. capacity per 2 km cell (20 MHz) 40 Mbps terrestrial
capacity per sq km 3.849002 Mbps eq. sat capacity needed per sat
beam 77388.77 Mbps
Satellite Carrier to Interference Ratio (C/I) and Satellite
Spectrum Reuse.
[0084] According to example embodiments, the following table
illustrates a typical example of reuse and C/I ratio (the required
SNR of a bearer that can close links for a given reuse value has to
be lower than the C/I specified in the table, and C/I mitigation
techniques, such as adaptive beam-forming and interference
cancellation, can be employed to achieve improved spectral
efficiency):
TABLE-US-00013 Typical Beam C/I Typical Beam C/I Typical Coverage
C/I Reuse (top 5%) (bottom 5%) (bottom 5%) 1 -7.5 dB -7.9 dB -8.5
dB 4 1.36 dB 0.965 dB -0.35 dB 7 7.6 dB 6.9 dB 5.6 dB 9 11.02 dB
10.6 dB 7.9 dB 12 20.42 dB 18.42 dB 14.05 dB
[0085] FIG. 4A illustrates a typical satellite beam from an 18
meter reflector, according to example embodiments. FIG. 4B
illustrates a typical satellite beam in a K=1 scenario, according
to example embodiments. FIG. 4C illustrates a typical satellite
beam in a K=4 scenario, according to example embodiments. FIG. 4D
illustrates a typical satellite beam in a K=9 scenario, according
to example embodiments.
Fading Characteristics.
[0086] According to example embodiments, a Rician fading model with
a Line-of-Sight (LoS) component and a Multipath (MP) component is
employed, which is representative of a user/UT in an open
environment with clear view of the sky with no head blockage. The
fading characteristics will exhibit different characteristics
depending on, for example, whether the user is walking slowly (less
than 5 km/h).fwdarw.slow fading, or driving in a car (e.g., 100
km/h).fwdarw.fast fading. Further, for suburban and urban
environments, the Loo distribution model may be employed. The
following figures show representative fading distributions based on
a Rician fading model and the Loo model.
[0087] FIG. 5A illustrates an example of slow fading (e.g., in an
open environment), according to example embodiments. FIG. 5B
illustrates an example of fast fading (e.g., in an open
environment), according to example embodiments. FIG. 5C illustrates
an example of fading (e.g., in a typical suburban environment),
according to example embodiments. FIG. 5D illustrates an example of
fading (e.g., in a typical urban environment), according to example
embodiments.
Attribute Comparison to GMR-1 System.
[0088] The following two tables illustrate a comparison of certain
attributes between the system architectures and designs of example
embodiments of the present invention and the architectures and
designs of GMR-1 systems (as defined in the European
Telecommunications Standards Institute (ETSI) published GEO-Mobile
Radio Interface Specifications standard):
TABLE-US-00014 Current Embodiments GMR-1 of the Present Attribute
Systems Invention Benefit Notes Symbol Up to 234 Up to 17.4 Data
Rate supported goes Current generation Hughesnet Rates ksps Msps up
from 590 kbps to 80 (Ku & Ka band) systems Mbps per
polarization. operate from 1-225 Msps Polarization Dual in return;
Dual in return, Allows up to 160 Mbps Requires very high satellite
single in Dual in forward using 20 MHz wide carrier power,
especially for handheld forward in forward link terminals. Channel
1.35 1.15 Results in about 17% Proposed roll-off factor has Spacing
increase in spectral been deployed in VSAT and efficiency other MSS
systems Modulation .pi./2 BPSK .pi./2 BPSK Allows spectral
efficiency to 64 QAM has been .pi./4 QPSK .pi./4 QPSK go up to 4.17
b/s/Hz per implemented for other MSS 16 APSK 16 APSK polarization;
8.34 b/s/Hz systems 32 APSK 32 APSK using both polarizations in [64
QAM] forward link FEC Convolutional Convolutional About 0.25 dB
improvement algorithm Turbo -- in links due to long code LDPC
(short LDPC (long blocks code blocks) code blocks) Reuse 1 to 19 1
to 19 Reuse of 1 used for CDMA Factors (fixed) (dynamic) based
system
TABLE-US-00015 Current Embodiments GMR-1 of the Present Attribute
Systems Invention Benefit Notes MIMO/Divers LEO Combination of with
LEO/MEO/ LEO/MEO/GEO GEO Adaptive Beam No Yes Improved C/I
performance Forming Successive No Yes Improved C/I performance
Interference Cancellation Faster Than No Yes [25%] improvement in
Implemented on VSAT Nyquist (FTN) throughput systems Carrier No Yes
Improves capacity about two- Aggregation fold assuming 34 MHz of L-
band and 30 MHz of 5-band Terrestrial No Possibly Higher link
margin and Provides capability to Extensions capacity in urban and
receive from satellite and suburban environments rebroadcast
terrestrially.
Long Term Evolution (LTE) VoIP Capacity.
[0089] The following table specifies a summary of LTE VoIP uplink
(UL) and downlink (DL) capacity--taken from the 3GPP specification
TR 25.912 (ver. 9.0.0)--assuming 5 MHz of spectrum, AMR codec up to
12.2 Kbps, which translates to approximately 12.2*300/500=0.7
bit/s/Hz:
TABLE-US-00016 TABLE 13.8 Summary of UL and DL VolP Capacity
Average VolP Capacity Deployment (users/sector) Scenario DL UL
Case1 317 241 Case2 293 -- Case3 289 123
Average Spectral Efficiency.
[0090] The following table specifies average spectral
efficiency--taken from the 3GPP specification 36.913 (ver. 12.0.0,
release 12):
TABLE-US-00017 TABLE 8.1 Targets for average spectrum efficiency
Radio env. Case 1 Rural/ Ant. Config. [bps/Hz/cell] Micro Indoor
High speed UL 1 .times. 2 1.2 2 .times. 4 2.0 DL 2 .times. 2 2.4 4
.times. 2 2.6 4 .times. 4 3.7
Vocoder Comparison.
[0091] FIG. 6A illustrates a comparison of example vocoders (taken
from the website http://www.dvsinc.com/papers/eval_results.htm).
FIGS. 6B(i), 6B(ii), 6B(iii), 6B(iv) illustrate a comparison of
example AMR and AMBE+2 vocoders (P25: AMBE+2 vocoder at 4.4 kbps
source rate; A12.2: AMR 12.2 kbps source rate; A7.4: AMR 7.4 kbps
source rate). The 6B figures show intelligibility results for ten
"audiometrically normal" subjects, with environments 1-4, showing
statistical similarities.
GMR-1 Bearer Table.
[0092] The following table, for example, shows a bearer table for a
GMR-1 system:
TABLE-US-00018 E.sub.s/N.sub.o Approx. Estimate Peak in static
Coding Payload AWGN Achievable Rate Bit Rate channel spectural
Modulation FEC (Approx.) (kbps) (dB) FER efficiency PI/4 QPSK Conv.
4/5 4 7.05 1.00E-02 1.19 PI/4 QPSK Conv. 1/2 2.45 3.55 1.00E-02
0.73 PI/4 QPSK Conv. 2/5 4 2.15 1.00E-02 0.59 PI/2 BPSK Conv. 1/2
2.45 -0.05 1.00E-02 0.36 PI/4 QPSK Conv. 3/5 21 5.55 1.00E-03 0.78
PI/4 QPSK Conv. 7/10 25 6.65 1.00E-03 0.93 PI/4 QPSK Conv. 4/5 29
7.95 1.00E-03 1.08 PI/4 QPSK Turbo 3/5 47 4.75 1.00E-03 0.87 PI/4
QPSK Turbo 7/10 56 6.15 1.00E-03 1.04 PI/4 QPSK Turbo 4/5 64 7.55
1.00E-03 1.19 PI/4 QPSK Turbo 1/2 110 2.65 1.00E-03 0.82 PI/4 QPSK
Turbo 5/8 139 3.85 1.00E-03 1.03 PI/4 QPSK Turbo 3/4 166 5.75
1.00E-03 1.23 PI/4 QPSK Turbo 5/8 186 6.95 1.00E-03 1.38 16 APSK
Turbo 1/2 222 9.2 1.00E-03 1.85 16 APSK Turbo 4/7 256 [10.1]
1.00E-03 1.90 16 APSK Turbo 2/3 296 11.8 1.00E-03 2.20 PI/4 QPSK
Turbo 5/8 261 4.15 1.00E-03 0.97 16 APSK Turbo 2/3 590 12.1
1.00E-03 2.19 PI/4 QPSK Turbo 1/2 261 2.95 1.00E-03 0.97 PI/4 QPSK
Turbo 3/4 261 6.05 1.00E-03 0.97 PI/4 QPSK Turbo 5/8 261 7.25
1.00E-03 0.97 32 APSK LDPC 4/5 444 16 1.00E-03 3.30
Capacity Density.
[0093] The following table illustrates terrestrial and satellite
capacity density equivalents:
TABLE-US-00019 Data Attribute Value Units circular area with cell
radius of 2 km 12.57 sq km circular area with sat beam radius of
20106.193 sq km 80 km avg. capacity per 2 km cell (20 MHz) 40 Mbps
terrestrial capacity per sq km 3.18 Mbps/sq_km eq. sat capacity
needed per sat beam 64 Gbps/sat_beam
[0094] The following table illustrates the effective capacity
density improvement required for satellite systems:
TABLE-US-00020 Data Attribute Value Units circular area with cell
radius of 2 km 12.57 sq km circular area with sat beam radius of
20106.193 sq km 80 km avg. capacity per 2 km cell (20 MHz) 40 Mbps
terrestrial capacity per sq km 3.18 Mbps/sq_km eq. sat capacity
needed per sat beam 64 Gbps/sat_beam Avg. achievable per sat beam
(20 MHz, 3.33 Mbps reuse 12) Improvement Factor Needed 19200
[0095] The following table illustrates the effective capacity
density improvement required for satellite systems in terrestrial
environments:
TABLE-US-00021 Data Attribute Value Units circular area with cell
radius of 2 km 12.57 sq km circular area with sat beam radius of
20106.193 sq km 80 km avg. capacity per 2 km cell (20 MHz) 40 Mbps
terrestrial capacity per sq km 3.18 Mbps/sq_km eq. sat capacity
needed per sat beam 64 Gbps/sat_beam Avg. achievable per sat beam
(20 MHz, 3.33 Mbps reuse 12) Improvement Factor Needed 19200 Extra
Link Margin for Terrestrial use 20 dB Effective Improvement Needed
1920000
[0096] The total land area of the contiguous United States is
approximately 7,600,000 km.sup.2, and, with an average of 3 Mbps
per km.sup.2, the total throughput for the United States would be
approximately 23 terra-bits per second (Tbps). According to example
embodiments, such a 23 Tbps system may comprise a total number of
approximately 10,000 LEO satellites globally. By way of example,
the satellites may be deployed in 66 orbits with 150 satellites per
orbit. By way of further example, hundred and 50 of such satellites
may cover the US with a throughput per satellite of 150 Gbps. By
way of further example, with a 2 GHz Ku availability in the forward
link and a reuse of 4, and with 60 beams per satellite and each
beam having 500 MHz of spectrum, an effective spectrum or capacity
of 30 GHz per polarization may be obtained--60 GHz of spectrum
using two polarizations. By way of further example, with a 16 APSK,
Rate 3/4 modulation and coding scheme, a spectral efficiency of 150
Gbps/60 GHz=2.5 can be achieved. By way of further example, such a
system may have an Es/No of 11 dB and a C/I of approximately 15 dB
with a reuse of 4. By way of further example, the UT may deploy a
tracking antenna of an approximate 70 cm aperture, in the system
would employ predictive handovers to assist signaling.
Synchronization.
[0097] According to example embodiments, the UT forward link
acquisition process may be in one of the following states: (1) Cold
Start--characterized by limited availability of satellite ephemeris
and/or terminal position data, resulting in large uncertainties in
Doppler and timing and antenna tracking angle--which is facilitated
by a terminal receiver that employs a large time, frequency,
angular acquisition window; (2) Warm Start--characterized by
available satellite ephemeris and/or terminal position data that
may not have been recently updated--links in partially synchronized
state; (3) Steady State (Idle and Connected Mode
Handovers)--characterized by available accurate ephemeris data, and
estimates of delay and Doppler and antenna tracking angle--guard
bands and acquisition windows are smallest. A UT forward link
synchronization scheme is employed to address these various modes
of operation.
[0098] According to example embodiments for the UT forward link
synchronization, the following synchronization schemes are
employed. According to one such embodiment, the satellite and the
UT both have a GPS disciplined oscillator, whereby the frequency
reference is locked to GPS, the frame markers are derived based on
GPS 1 pps timing ticks, and the UT continually estimates the
downlink delay and Doppler using the satellite ephemeris data.
According to a further such embodiment, downlink timing is acquired
at the UT, where, by adding the estimated downlink delay to its GPS
based 1 pps ticks, the UT derives an estimate of the downlink frame
markers, and the UT opens an acquisition window for the downlink
frame timing around this estimated frame marker (the acquisition
window is largest at cold start (e.g., may be continuous), smaller
in the warm start, and smallest in steady-state). According to a
further such embodiment, downlink frequency is acquired at the UT,
where, by adding the estimated downlink Doppler to its GPS
disciplined frequency reference, the UT derives an estimate of the
downlink frequency, and the UT opens an acquisition window centered
at this estimated downlink frequency (the acquisition window is
largest at the cold start (e.g., may be continuous), smaller in the
warm start, and smallest in steady-state). After the initial
acquisition, the downlink timing and frequency are continually
tracked by the UT receiver.
[0099] In TDMA systems, different non-collocated terminals occupy
different timeslots of the return link frame. According to example
embodiments, therefore, for the UT return link synchronization, the
synchronization scheme is designed so to ensure that the uplink
transmissions of different terminals do not overlap or collide at
the satellite. For example, if different terminals apply a constant
offset to its receive frame marker to determine its transmit frame
marker, their respective uplink transmissions may collide at the
satellite. FIG. 7A illustrates an example of UT return link
synchronization where the transmissions of two different UTs
overlap at the satellite. As shown in the figure, since the two
terminals apply a constant TRO independent of their RTT latencies,
their respective uplink transmissions collide in the return link
frame at the satellite.
[0100] FIG. 7B illustrates an example UT return link
synchronization scheme, according to example embodiments. According
to example embodiments, the UT continually adjusts the Transmit
Receive Offset (TRO) to make it equal to the negative of its RTT
latency plus a system constant. In this manner, each terminal
applies a time-varying TRO equal to the negative of its own RTT
latency, plus a system constant K, which ensures that their
respective uplink transmissions fit in the assigned slots of the
return link frame at the satellite.
[0101] FIG. 8A illustrates synchronization and half-duplex
operation for a beam level, position unaware scheduler, and FIG. 8B
illustrates synchronization and half-duplex operation for a
terminal position aware scheduler. With reference to FIG. 8A, for a
single allocated uplink burst, the same set of downlink bursts is
blocked irrespective of the terminal position within the beam, and
the number of blocked bursts varies from beam to beam. With
reference to FIG. 8B, the number of blocked bursts is reduced,
because the scheduler accounts for the terminal specific TRO, and
the downlink bursts that are blocked depends on the terminal
position within the beam.
[0102] FIG. 9 illustrates a further example synchronization scheme,
according to example embodiments. At Step 1, the satellite
broadcasts on the Control Channel the ephemeris vectors of all
satellites (e.g., LEO satellites). At Step 2, the UT acquires the
forward link Control Channel and reads the broadcast ephemeris
information. At Step 3, the UT initiates a connection by
transmitting an Contention burst on the return link random access
channel (RACH). At Step 4, the satellite acquires the RACH Probe
from the UT and measures the received timing and frequency. At Step
5, the Gateway (GW) sends to the UT the Immediate Assignment
message on the Access Grant Channel (AGCH), which may optionally
contain a timing and frequency correction field. At Step 6, the UT
receives the AGCH message. At Step 7, the UT initiates the Return
Traffic Channel (RTC). At Step 8, the GW seeds the RTC receiver
using the measured timing offset measured on the RACH, and
initiates the Forward Traffic Channel (FTC). Further, to conserve
battery, the UT may enter the sleep mode at Steps 2 and 7.
[0103] According to further example embodiments, the terminal uses
a predictive approach to determine the expected [time, frequency]
offsets of the downlink burst after wake up (e.g., after the UT
wakes from the sleep mode entered in the idle and connected modes).
By way of example, the terminal determines the [time, frequency]
offset of the last downlink burst read prior to entering the sleep
mode, and then enters the sleep state for the next consecutive N
downlink bursts. Then, just prior to the next downlink burst that
the terminal must receive, the terminal wakes up and extrapolates
[time, frequency] offsets measured for the last received burst
using the ephemeris knowledge.
[0104] FIG. 10 illustrates an example terminal schematic and sleep
states, according to example embodiments. For example, by keeping
the terminal clock active while the other modules of the terminal
circuitry go to sleep, the terminal frame numbering and frequency
synch is kept in a disciplined state on wake-up.
[0105] FIG. 11A illustrates the rate of change of delay on LEO
links, and FIG. 11B illustrates the rate of change of Doppler on
LEO links, according to example embodiments. By way of example,
rates of change of delay and Doppler on the LEO links have been
determined to be at maximum uncertainties in rates of change of
delay of .+-.12.5 ppm, and rates of change of Doppler of .+-.0.04
ppm/sec.
[0106] FIG. 11C illustrates uncertainty in delay as a function of
terminal sleep duration, and FIG. 11D illustrates uncertainty in
Doppler as a function of terminal sleep duration, according to
example embodiments. For example, The duration of the terminal
sleep state and the predictability of satellite motion when
terminal is in the sleep state determine the uncertainties at the
terminal in delay and Doppler after the terminal wakes from the
sleep state. The FIGS. 11C and 11D show example profiles of the
delay and Doppler uncertainties, taking an example model of
ephemeris knowledge (e.g., when the ephemeris is known at the
terminal, the delay uncertainty at the highest bandwidth of 500 MHz
reduces to a few symbols from a few hundred symbols).
[0107] According to example embodiments, certain design
considerations are applied to address link outages. The terminal
performs a link outage detection (signal present versus signal
absent) check for each burst it receives. Further, due to the
possibility of a link outage when the terminal wakes from a sleep
state, the duration since it last successfully acquired a downlink
burst can be greater than the duration of the sleep state. In case
of a link outage, with regard to delay and Doppler uncertainties,
the terminal expands its time and frequency domain acquisition
ranges based on (i) the duration since last successful burst
acquisition, and (ii) the expected uncertainties in the rates of
change of delay and Doppler. Further, the terminal may include an
extra margin in the acquisition ranges to guard against the
possible drift in the terminal local timing and frequency
references during its sleep state.
[0108] According to further example embodiments, in addition to
simplifying the forward link burst acquisition at the terminal
after it wakes from a sleep state, the knowledge of ephemeris at
the terminal additionally helps simplify the return link burst
acquisition at the satellite. By way of example, the following
table illustrates example return link burst acquisition ranges at
the satellite (SAT):
TABLE-US-00022 Round Trip Frequency Uncertainty Type of Return Link
Round Trip Delay in kHz Window at SAT Uncertainty in ppm (at Ku
Band) Satellite Link Aperture .+-.620 .mu.s .+-.26.66 ppm .+-.363.2
kHz Beam Width Aperture .+-.440 .mu.s .+-.5.28 ppm .+-.71.9 kHz
Wide Aperture .+-.30 .mu.s .+-.0.3 ppm .+-.4.1 kHz Normal Aperture
.+-.2 .mu.s .+-.0.05 ppm .+-.0.7 kHz
[0109] In the table, the wide aperture and normal aperture rows are
with ephemeris knowledge, and the satellite link aperture and beam
width aperture rows are without ephemeris or position knowledge. In
the connected mode, the normal aperture affects the frequency of
the closed loop corrections (CLCs) to the UT Transmit Receive
Offset (TRO), and the UT extrapolates the received TRO on the CLC
using the ephemeris data to remain within the normal aperture. For
initial contention access, the wide aperture is determined by the
accuracy of the ephemeris model. The beam width aperture and
satellite link aperture are required if the ephemeris knowledge is
not available, and are included in the table for comparison. With
the known ephemeris, the window sizes for return link burst
acquisition at the satellite reduce by an order of magnitude.
Accordingly, the wide aperture is chiefly determined by the
accuracy of the ephemeris model and the terminal position
knowledge--in the example numbers of the foregoing table, the
allocated budget for ephemeris errors (in estimation of RT delay
and RT Doppler) is .+-.30 is and .+-.0.3 ppm, respectively.
[0110] The Normal and Wide Apertures described above are
interrelated. The normal aperture affects the frequency of the
closed loop corrections (CLCs) to UT's Transmit Receive Offset
(TRO). For example, the RT Doppler error induced rate of change of
.+-.0.3 ppm, and the normal aperture of .+-.2 is . . . one CLC may
be needed .about.2/0.3=6.6 seconds. Further, the Normal Aperture
reduces with (i) increasing accuracy of the ephemeris, and (ii) an
increase in the maximum rate at which the CLCs are sent. For (ii)
above, the ETSI GMR-1 3G standard provides for a periodically
dedicated uplink resource, which may be considered for a LEO
satellite System.
[0111] Additionally, to support the "lost terminal" whose position
is not available, the beam width aperture may be needed. For
example, by using the estimate of the RTT latency and the RTT
Doppler provided by the satellite (based on its beam width
aperture), the "lost terminals" may be able to fix their positions.
However, along the satellite ground track, the rate of change of RT
Doppler is small, causing a high Geometric Dilution of Precision
(GDOP). This issue can be addressed either by performing
triangulation using multiple satellites, or by allowing for an
increased delay in the position fix.
[0112] As shown above, accurate knowledge of ephemeris at the
terminal helps simplify the burst acquisition after the terminal
wakes up from a sleep state, after warm start, and at satellite and
beam handovers. In that context, according to example embodiments,
the following consist of an example set of requirements for the LEO
satellite ephemeris: 1.sigma. accuracy of satellite ephemeris
position .about.50 meters, and of satellite ephemeris velocity
.about.0.05 meters/sec. This accuracy facilitates an efficient
design--for example, regarding UT and satellite acquisition and
tracking mechanisms, handover mechanisms, paging mechanisms, etc.
Further, the on-board timing and frequency references can be
disciplined using the on-board GPS system at the satellite, which
allows the on-board references to be highly stable (e.g., drift of
less than 10.sup.-11), and simplifies terminal forward link
acquisition at cold/warm start.
[0113] According to example embodiments, the format of the
ephemeris model is a parametric set with the following
parameters--argument of latitude L, inclination i, longitude of
ascending node fl, radius r. By way of example, each set of
parameters may be valid for one orbit duration (e.g., about 100
minutes). The satellite position and velocity vectors in ECEF
coordinates can be computed using the above orbit parameters at any
given time using the following matrix equation:
p = [ cos L cos .OMEGA. - sin L sin .OMEGA. cos i cos L sin .OMEGA.
- sin L cos .OMEGA. cos i sin L sin i ] ##EQU00001##
[0114] Accordingly, each day, approximately 30 such sets are
provided that cover a period of the next approximately two days.
Further, such a format of the ephemeris simplifies transmission on
the forward link broadcast control channel, where the ephemeris
broadcast can be achieved in a highly compressed and extremely
accurate manner.
MIMO for Satellite Links.
[0115] In radio, multiple-input/multiple-output (MIMO) is a method
for multiplying the capacity of a radio link using multiple
transmit and receive antennas to exploit multipath propagation.
MIMO has become an essential element of wireless communication
standards including IEEE 802.11n (Wi-Fi), IEEE 802.11ac (Wi-Fi),
HSPA+(3G), WiMAX (4G), and Long Term Evolution (4G). More recently,
MIMO has been applied to power-line communication for 3-wire
installations as part of ITU G.hn standard and HomePlug AV2
specification.
[0116] According to example embodiments, channel capacity is
improved through the application of MIMO techniques.
[0117] For single user applications, there are various channel
capacity formulations.
[0118] Single-user single-input/single-output (SU-SISO) channel
capacity in a Rayleigh channel is a random variable given as (e.g.,
if channel h is Rayleigh, SNR is multiplied by a Chi-squared
variable with 2 degrees of freedom):
C=log.sub.2(1+SNR*X.sub.2.sup.2)
[0119] Single-user single-input/multiple-output (SU-SIMO) channel
capacity in a Rayleigh channel with n.sub.R receive antennas is
(thus, there is an SNR gain, because of increased degrees of
freedom of Chi-squared variable):
C=log.sub.2(1+SNR*X.sub.2.times.n.sub.R.sup.2)
[0120] Single-user multiple-input/multiple-output (SU-MIMO) channel
capacity in a Rayleigh channel with n.sub.R receive antennas and
n.sub.T transmit antennas (total Tx power constraint of
P.sub.T):
C = log 2 [ det ( I n R + P T n T .sigma. 2 * HH + ) ] = log 2 [
det ( I n R + SNR n T * HH * ) ] ##EQU00002##
whereby, for a given n.sub.R, as n.sub.T gets large,
1 n T HH + -> I n R , ##EQU00003##
and thus,
C=n.sub.R log.sub.2[1+SNR], or alternatively R=n.sub.RB
log.sub.2[1+SNR]
Therefore, the original channel dimension (degrees of freedom) of B
is multiplied by n.sub.R--which reflects a dimensionality gain that
translates to a more impressive outcome than SNR gain.
[0121] For a further MIMO channel capacity formulation, let
Rank(H)=k.ltoreq.min(n.sub.T, n.sub.R), and {.lamda..sub.i} denote
singular values of H--an alternative formulation for MIMO channel
capacity is:
C = i = 1 k log 2 ( 1 + SNR * .lamda. i / n T ) ##EQU00004##
where a rule of thumb for an upper bound for the channel capacity
is:
C.ltoreq.k*log.sub.2(1+SNR*u)
where u is a random variable determined by singular values of H,
and there is a linear multiplicative, instead of logarithmic, gain
in C.
[0122] FIG. 12A illustrates the ergodic capacity of a Rayleigh
fading SISO channel (dotted line) compared to the Shannon capacity
of a SISO channel (solid line). FIG. 12B illustrates the Shannon
capacity of a SISO channel (dotted line) compared to the ergodic
capacity of a Rayleigh fading MIMO channel (solid line) with
n.sub.T=n.sub.R=6. FIG. 12C illustrates a comparison between
channel capacity of SISO, SIMO and MIMO channels. In general,
channel capacity can increase n fold with n.times.n MIMO.
[0123] According to example embodiments, for the model of a channel
with inter-symbol interference (ISI), a received signal in the
presence of ISI can be formulated as:
y ( n ) = k = 0 L - 1 h k b ( n - k ) ##EQU00005##
where, [h.sub.0, h.sub.1, . . . , h.sub.L-1].sup.T is a L.times.1
vector of channel coefficients, and b=[b(0), b(1), . . . ,
b(N.sub.b-1)] is an N.sub.b.times.1 vector of transmit signals.
[0124] This convolution operation can alternatively be represented
in Matrix formulation as follows:
y=H.times.b
[0125] Accordingly, with the model of a channel with ISI, the input
symbol vector b is passed through the channel matrix H with ISI
(e.g., multipath, FTN, etc.), and the received vector y=H.times.b,
where the channel matrix H is as follows:
H = [ h 0 0 h 1 h 0 h 2 h 1 0 h L - 1 h 1 h 0 ] N b N b
##EQU00006##
[0126] Eigen-Decomposition of the Channel with ISI:
[0127] The channel with ISI is an LTI system, which has the complex
exponentials (sinusoids) as its eigenfunctions. For this property
to hold, however, N.sub.b is required to be infinite--unless matrix
H is converted to the following circulant matrix (each row is the
prior row right shifted by one, with several nonzero elements added
in upper right corner, as follows (which is achieved by adding a
cyclic prefix to the vector b:
##STR00001##
[0128] View of Orthogonal Frequency-Division Multiplexing (OFDM) as
Linear Precoding:
[0129] Where N.sub.b.times.N.sub.b channel matrix H is decomposed
according to eigen-decomposition: H=VAV.sup.+. V is an
N.sub.b.times.N.sub.b matrix of eigen-vectors of H (i.e., complex
exponentials in DFT transformation), and A is a diagonal matrix of
N.sub.b eigenvalues (i.e., the DFT coefficients of channel vector
h). DFT Precoding in OFDM: Given an N.sub.b.times.1 vector b of
transmission symbols, DFT precoding in OFDM transforms b to an
N.sub.b.times.1 vector b': b'=Vb.
[0130] FIG. 13 illustrates a view of OFDM as linear precoding,
according to example embodiments. The received signal
N.sub.b.times.1 vector is given as y=Hb'+n. The receiver applies
linear transformation C.sup.+=V.sup.+ (i.e., the IDFT) to y to
obtain
y'=C.sup.+y=V.sup.+Hb'+V.sup.+n=V.sup.+V.LAMBDA.V.sup.+Vb+n'=.LAMBDA.b+n'-
. By applying DFT precoding, the channel with ISI
(cross-connectivity across symbols) is transformed into a diagonal
channel without ISI.
[0131] According to further example embodiments, architectures and
designs are provided to claim the full capacity benefit of MIMO
techniques. By way of example, analogous to DFT-based precoding
described above, the MIMO matrix with full connectivity is
diagonalized by eigen or singular value decomposition--where,
unlike cyclic prefix operation in OFDM, there is not any method to
convert MIMO matrix into a circulant matrix, thus, to achieve this
diagonalization, unlike the OFDM scheme, both the transmitter and
the receiver need to have the knowledge of channel matrix H.
[0132] According to one such embodiment, where the
n.sub.R.times.n.sub.T channel matrix H is decomposed according to
eigen decomposition--H.sup.+H=V.LAMBDA.V.sup.+-V is an
n.sub.T.times.n.sub.T matrix of eigen-vectors of H.sup.+H, and
.LAMBDA. is a diagonal matrix of n.sub.T eigenvalues. The MIMO
Precoding is as follows: given an n.times.1 vector b of
transmission symbols, where n.ltoreq.n.sub.T, the MIMO precoding
scheme transforms b to an n.sub.T.times.1 vector b'
(b'=V.sub.nAb)-V.sub.n is an n.sub.T.times.n matrix with n vectors
of V corresponding to nonzero eigenvalues in .LAMBDA., and A is an
n.times.n diagonal matrix that allocates power across n parallel
data streams. The received signal n.sub.R.times.1 vector is given
as y=Hb'+n. The receiver applies linear transformation
C.sup.+=AV.sub.n.sup.+H.sup.+ to y to obtain
y'=C.sup.+y=AV.sub.n.sup.+H.sup.+Hb'+C.sup.+n=AV.sub.n.sup.+H.sup.-
+HV.sub.nAb+n'=.LAMBDA.A.sup.2b+n'. Thus, the interference caused
by MIMO channel is completely eliminated because of the use of an
appropriate precoding matrix V.sub.nA at the transmitter and a
receiver "filter" C=AV.sub.nH at the receiver. Accordingly, such
MIMO precoding provides optimal capacity gain due to MIMO with a
very simple receiver architecture, and channel coding schemes for
SISO channel work "as-is," and provide the same performance gain as
the more complicated space-time coding.
[0133] According to example embodiments, such approaches are
applicable to the satellite forward link, as follows: (i) vector b
is available at the Gateway (Forward link bit streams of different
users); (ii) assuming LOS channel without diffuse component, matrix
H is available at the Gateway (secondary feed elemental gain
vectors for different users); (iii) however, the k.sup.th user sees
only one element, y.sub.k, of vector y--a central processing entity
is therefore employed, which collects different elements of y from
different users, has knowledge of H and V.sub.n matrices used at
the transmitter, applies linear transformation C to y, and sends
elements of y' back to corresponding users.
[0134] Further, such approaches are also applicable to the
satellite return link, as follows: (i) the concept of the central
processing entity can be extended to enable similar precoding
scheme for the return link transmissions from different users.
[0135] Further, such approaches may also applicable to other
interference-rich scenarios such as FTN, NOMA, etc., as follows:
(i) interpretation of Matrix H varies (matrix of ISI terms for FTN,
matrix of CCI terms for NOMA, etc.) but the algebra remains the
same.
[0136] Several studies in the literature have addressed MIMO over
satellite, such as Dual polarization SU-MIMO, SU-MIMO with
geographically separated ground stations, MIMO with multiple
coordinated satellites, Multiuser MIMO over satellite.
[0137] FIG. 14A illustrates an example of Dual Polarization
SU-MIMO, and FIG. 14B illustrates an example of SU-MIMO with
geographically separated ground stations. FIG. 14C illustrates an
example of Dual Polarization MIMO over Land Mobile Satellite
Systems. A single satellite employs a dual circularly polarized
antenna, and the UT similarly has a dual circularly polarized
antenna. S (2/4 GHz) band, geostationary orbit (GEO), and MIMO
channel has a LOS component and a diffuse component.
[0138] The following table illustrates parameters assumed for
Dual-Polarized MIMO LMS channel scenarios.
TABLE-US-00023 Parameter Open Rural Environment Suburban
Environment Urban Environment Reference Operating frequency, f 2.2
GHz (S band) 2.2 GHz (S band) 2.2 GHz (S band) [9] Satellite orbit
GEO GEO GEO [9] Polarization RHCP & LHCP RHCP & LHCP RHCP
& LHCP [9] Mobile UT speed, .upsilon. 50 km/h 50 km/h 50 km/h
[9] Satellite elevation angle, .theta. 40.degree. 40.degree.
40.degree. [9] XPD of environment, XPC.sub.env 15 dB 6 dB 5 dB [8],
[17] XPD of UT antenna, XPD.sub.ant 15 dB 15 dB 15 dB [8], [17] Loo
statistical parameter For each environment, each time a new state
is reached, (.alpha., .psi., MP) [14] triplet (.alpha., .psi., MP)
are drawn from corresponding joint distribution Polarization
correlation coefficient 0.4 0.5 0.5 [8], [17] of small-scale fading
components at Tx, .rho..sub.tx Polarization correlation coefficient
0.5 0.5 0.5 [8], [17] of small-scale fading components at Tx,
.rho..sub.rx Polarization correlation matrix of large-scale fading
components, C [ 1 0.80 0.85 0.00 0.80 1 0.01 0.87 0.85 0.91 1 0.88
0.90 0.87 0.88 1 ] ##EQU00007## [ 1 0.76 0.70 0.83 0.76 1 0.83 0.75
0.70 0.83 1 0.78 0.83 0.75 0.78 1 ] ##EQU00008## [ 1 0.86 0.80 0.92
0.86 1 0.89 0.85 0.86 0.89 1 0.93 0.92 0.85 0.93 1 ] ##EQU00009##
[6] Inter-state temporal variations For each environment,
first-order 2-state Markov chain model with respective absolute
state [14] and state transitions probability matrices W.sub.MIMO =
W.sub.SISO and P.sub.MIMO = P.sub.SISO
[0139] FIG. 15A illustrates a channel capacity example in a rural
environment. As cross-polarization discrimination of UT antenna
increases, the cross-polar interferences become weaker, the MIMO
channel becomes diagonal and the outage capacity achieved
increases.
[0140] FIG. 15B illustrates a channel capacity example in a
suburban environment. As satellite elevation reduces, the blockage
probability decreases and MIMO capacity reduces.
[0141] FIG. 15C illustrates a channel capacity example in a
suburban environment. A significantly reduced MIMO capacity exists
in urban environment. If polarization correlation coefficient is
low (e.g., around 0.1), for the diffuse component, MIMO can provide
ten-fold increase in the capacity. A typical polarization
correlation coefficient is around 0.5.
[0142] FIG. 15D illustrates modeling and performance evaluation of
a land mobile satellite dual polarized MIMO channel along roadside
trees. The following table lists the MIMO shadowing correlation
coefficients obtained from simulations:
TABLE-US-00024 TABLE I MIMO SHADOWING CORRELATION COEFFICIENTS
OBTAINED FROM FDTD SIMULATIONS R/R L/L R/L L/R R/R 1 0.87 0.30 0.43
L/L 0.87 1 0.26 0.47 R/L 0.30 0.26 1 0.49 L/R 0.43 0.47 0.49 1
[0143] FIG. 16A and FIG. 16B illustrate a multi-satellite MIMO
example at Ka band and above. FIG. 16A shows a configuration of a
dual-satellite 2.times.2 MIMO channel, where i Individual
satellites S.sub.1 and S.sub.2 transmit either independent data
streams (MIMO spatial multiplexing system) or the same signal over
the multiple independently fading paths (MIMO diversity system),
and FIG. 16B shows the associated elevation angles. FIG. 16C
illustrates channel capacity of a dual satellite MIMO. The capacity
may be formulated as:
C = i = 1 2 log 2 ( 1 + SNR i 2 * 10 - A R i / 10 )
##EQU00010##
[0144] For multi-user MIMO, based on applying either a linear
(e.g., MMSE) or nonlinear (e.g., Tomlinson-Harashima) precoding at
the transmitter, the following table shows a performance comparison
of various satellite multi-beam precoding techniques (MIMO over
Satellite: A Review, By Arapalogou et al., IEEE Communications
Surveys and Tutorials, 2011):
TABLE-US-00025 TABLE IV PERFORMANCE COMPARISON OF VARIOUS SATELLITE
MULTIBEAM PRECODING TECHNIQUES [120]. Rate Availability Rate
(bps/Hz) (%) Variance Reference Beam 1 2.55 96.3 1.35 Beam 4 1.45
92.7 0.16 Aggregate 16.80 95 1.19 MMSE Beam 1 3.16 84.9 4.24 Beam 4
1.89 74.8 1.63 Aggregate 20.90 83.7 3.89 MOB Beam 1 0.86 43.0 0.11
Beam 4 0.86 42.5 0.11 Aggregate 6.04 42.7 0.11 IMOB Beam 1 8.09 100
3.74 Beam 7 2.19 87.6 0.74 Aggregate 24.40 95.5 1.12
[0145] While example embodiments of the present invention may
provide for various implementations (e.g., including hardware,
firmware and/or software components), and, unless stated otherwise,
all functions are performed by a CPU or a processor executing
computer executable program code stored in a non-transitory memory
or computer-readable storage medium, the various components can be
implemented in different configurations of hardware, firmware,
software, and/or a combination thereof. Except as otherwise
disclosed herein, the various components shown in outline or in
block form in the figures are individually well known and their
internal construction and operation are not critical either to the
making or using of this invention or to a description of the best
mode thereof.
[0146] In the preceding specification, various embodiments have
been described with reference to the accompanying drawings. It
will, however, be evident that various modifications may be made
thereto, and additional embodiments may be implemented, without
departing from the broader scope of the invention as set forth in
the claims that follow. The specification and drawings are
accordingly to be regarded in an illustrative rather than
restrictive sense.
* * * * *
References